package forkjoin;

import java.util.concurrent.*;

public class CountTask extends RecursiveTask<Integer> {
    private static final int THRESHOLD = 2; //阈值
    private int start;
    private int end;

    public CountTask(int start, int end) {
        this.start = start;
        this.end = end;
    }

    @Override
    protected Integer compute() {
        int sum = 0;
        //如果任务足够小就计算任务
        if ((end - start) <= THRESHOLD) {
            for (int i = start; i <= end; i++) {
                sum += i;
            }
        } else {
            //如果任务大于阀值，就分裂成两个子任务计算
            int middle = (start + end) / 2;
            CountTask leftTask = new CountTask(start, middle);
            CountTask rightTask = new CountTask(middle + 1, end);
            //执行子任务
            leftTask.fork();
            rightTask.fork();
            //等待任务执行完，并得到其结果
            int leftResult = leftTask.join();
            int rightResult = rightTask.join();
            //合并子任务
            sum = leftResult + rightResult;
        }
        return sum;
    }

    public static void main(String[] args) {
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        //生成一个计算任务，负责计算l+2+3+4
        CountTask task = new CountTask(1, 4);
        //执行一个任务
        Future<Integer> result = forkJoinPool.submit(task);
        try {
            System.out.println(result.get());
            do {
                System.out.printf("Main: Thread Count: %d\n", forkJoinPool.getActiveThreadCount());
                System.out.printf("Main: Thread Steal: %d\n", forkJoinPool.getStealCount());
                System.out.printf("Main: Parallelism: %d\n", forkJoinPool.getParallelism());
                try {
                    TimeUnit.MILLISECONDS.sleep(5);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            } while (!task.isDone());

        } catch (InterruptedException e) {
        } catch (ExecutionException e) {
        }
    }
}